Preheat the oven to 350 degrees F (180 degrees C). Grease a 9x13-inch baking pan with butter.
Melt the Butter (2 tablespoon) and Unsweetened Chocolate (2 ounce) together. I do this in a microwave-safe dish in the Panasonic Microwave Oven.
In a separate saucepan, heat Buttermilk (2 cup) gently until just a little warmer than body temperature - being careful not to boil or cook it. Remove from heat and set aside.
In a large mixing bowl combine All-Purpose Flour (2 1/2 cup), Brown Sugar (1 cup), Baking Powder (3 teaspoon), Baking Soda (1 teaspoon), and Salt (1/2 teaspoon). Mix well, making as uniform a mixture as possible.
Pour melted chocolate and butter into dry ingredients. Pour in buttermilk and Vanilla Extract (1 teaspoon). Stir until combined. Stir in Semi-Sweet Chocolate Chips (1 cup), if desired. Spread into the prepared pan.
Combine the remaining Brown Sugar (1 1/4 cup) with the Unsweetened Cocoa Powder (1/2 cup) (plus 2 Tbsp) in a small bowl. Sprinkle this mixture as evenly as possible over the top of the batter.
Pour on the boiling Water (2 1/2 cup). It will look terrible, and you will not believe you are actually doing this, but try to persevere.
Place immediately in the preheated oven. Bake for 30 to 40 minutes or until the center is firm to the touch.
Cool for at least 30 minutes before serving. Invert each serving on a plate so that the fudge sauce on the bottom becomes a topping. Serve hot or at room temperature. Cooking results may vary depending on microwave oven used.